Runtastic PRO is probably the best app for runners in the Windows Store. It helps you monitor all outdoor (running, walking, hiking, biking, etc.) and indoor (treadmill, cardio, yoga, weight lifting & more) health & fitness activities.
It also supports the Runtastic Wearable Connect feature, allowing you to use chest straps and other accessories.
Unfortunately the app has become another victim of Windows Phone’s falling market share, with the company announcing on their website that they have discontinued further updates for their apps, writing:
Windows Phone unfortunately has fewer users compared to Android and iOS. This means that the market is a relatively smaller one. Like any company, we make some of our decision based on where we see the greatest potential. And yet, we are one of the few companies that have developed apps for this platform.
Of course, we also want to provide our Windows Phone users with the best possible products. We ask for your understanding that our priorities are based on the platform and the market, and we are no longer updating our apps for Windows Phone.
The apps are still available in the store, and as far as we know are still supported, so existing users probably have no need to jump ship. If you are a windows phone user however and looking to start using an exercise tracking system it would probably be better to invest in Garmin or Fitbit, both of who have excellent UWP apps which are not likely to disappear soon, or Endomondo Sports Tracker, which have much the same features as Runtastic.